SiC is a material which is physically and chemically stable as evinced by abounding in thermal conductivity, generally excelling in thermal resistance and mechanical strength and tolerating radial rays and which has a broad energy band gap. Thus, it can be utilized as the material for an environment-proof device usable even at an elevated temperature, the material for a device resisting radiant rays, the material for a power device specializing in power control, the material for a short-wavelength light-emitting device, etc. In recent years, it has been attracting general attention as a power device specializing in power control and has been undergoing enthusiastic development.
For the purpose of disseminating the SiC single crystal as the material for the power device specializing in power control, this crystal is naturally required to be perfectly free from faults, such as dislocations. For the sake of lowering the cost of the device, it is as well required to be a wafer of a large diameter.
In order to manufacture this wafer having a large diameter and not suffering from any appreciable fault, a seed crystal that has a large diameter and a low defect density is an indispensable necessity.
The generally available SiC seed crystal excelling in quality, however, is a crystal (Lely crystal) that is made by the sublimation and recrystallization method using no seed crystal and called the Lely method. The Lely method incurs difficulty in enabling addition to diameter and barely allows the production of a crystal approximating to 1 cm2 at most.
The large SiC single crystal available to date has been produced by using the Lely crystal as a seed crystal, repeating growth of crystal in the same direction (mainly in the direction of the c-axis) by using the sublimation and recrystallization method called the modified Lely method, and enlarging the crystal in the direction of the a-axis little by little.
The enlargement of size in the direction of the a-axis, therefore, has necessitated a great deal of time. The production of a crystal measuring 2 inches from a crystal measuring approximately 1 inch, for example, has required time exceeding one year.
For the purpose of solving the problems mentioned above, methods for attaining growth of crystal by joining small seed crystals side by side like the case of tiles (refer to JP-A HEI 11-268989 and JP-A 2003-527298), a method for preparing a seed crystal by joining SiC single crystals (refer to JP-A 2001-253799), and a method that comprises growing cubic SiC on an Si substrate enabling production of a wafer of large diameter, depriving the grown cubic SiC of the Si substrate and then subjecting the cubic SiC to heat treatment, thereby converting it into hexagonal SiC, such as of a 4H-type (refer to JP-A HEI 11-268995), have been disclosed.
When what is obtained by joining small seed crystals is grown as a seed crystal or a substrate, the grown product has the quality thereof lowered by suffering crystal faults, such as dislocations or micropipes, to emanate from the boundary surface of the resultant joint. When a crystal of large diameter is obtained by using an Si substrate, this crystal cannot acquire a fully satisfactory quality because the crystal defect that occurs in consequence of mismatching between lattice constants of Si and SiC survives after the heat treatment.
This invention is aimed at providing a method for the production of an SiC single crystal that is capable of accomplishing enlargement of crystal efficiently without entailing a crystal defect.